A typical thin film transistor (TFT) is made of a substrate, a gate electrode, an insulation layer, a drain electrode, a source electrode, and a semiconducting layer. The thin film transistor performs a switching operation. In use, the thin film transistor modulate an amount of carriers accumulated in an interface between the insulation layer and the semiconducting layer from an accumulation state to a depletion state, with applied voltage to the gate electrode. Thus, the thin film transistor can change an amount of the current passing between the drain electrode and the source electrode. In practical use, a high carrier mobility affect by the material of the semiconducting layer of the thin film transistor is desired.
In prior art, the material of the semiconducting layer is amorphous silicone (a-Si), poly-silicone (p-Si), or organic semiconducting material. The carrier mobility of an a-Si TFT is relatively lower than a p-Si TFT. However, the method for making the p-Si TFT is complicated and has a high cost. The organic TFT is flexible but has low carrier mobility.
Carbon nanotubes (CNTs) are a novel carbonaceous material and received a great deal of interest since the early 1990s. Carbon nanotubes have interesting and potentially useful heat conducting, electrical conducting, and mechanical properties. Further, there are two kinds of carbon nanotubes: metallic carbon nanotubes and semiconducting carbon nanotubes determined by the arrangement of the carbon atoms therein. The carrier mobility of semiconducting carbon nanotubes along a length direction thereof can reach about 1000 to 1500 cm2V−1s−1. Thus, in prior art, a TFT adopting carbon nanotubes as a semiconducting layer has been produced. However, the the semiconducting layer prepared often includes many metallic carbon nanotubes except semiconducting carbon nanotubes, which will affect the performance of the semiconductor layer.
What is needed, therefore, is to provide a method for making a thin film transistor that can overcome the above disadvantages.